import java.util.Scanner;

public class Main {
    public static String fun(double n, int m) {
        String s = "%." + String.valueOf(m) + "f";
        return String.format(s, n);
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        double cur = n * 1.0;
        while (true) {
            double next = (cur + n * 1.0 / cur) / 2;
            if (Math.abs(cur - next) < 0.00001) {
                System.out.println(fun(next, 3));
                break;
            }
            cur = next;
        }
    }
}